The Simulation And Implementation Of Underwater Acoustic Networks

Underwater acoustic network is a kind of self-organizing network. The network who has important significance for military and civilian is mainly used for marine data acquiring, pollution monitoring, marine exploring, disaster warning, the auxiliary underwater vehicle navigation and etc.. However, due to the marine environment and the characteristics of underwater acoustic channel, achieving the establishment of a reliable high-speed underwater acoustic communication network still faces some problems, such as the complex channel conditions, costly test and complex equipment.The thesis is based on the underwater acoustic network simulation sofeware, and it begins with the basic theory of underwater acoustic communication network protocol stack, and the classification and characteristics of layers in the protocol stack are also analysed. In this thesis, the network layer and link layer in the underwater acoustic network protocol stack are designed and simulated with Visual C++6.0. Then, network layer with the characteristics of automatic networking and automatic routing maintenance is carried out with table driven approach. In the link-layer, the error control is carried out by automatic selective retransmission mechanism, through the handshake mechanism, the link-layer partly solves the hidden terminal and exposed terminal problems.Media access control sublayer in link-layer uses random accessing pattern, which improves the channel utilization. The performance of these layers'protocol are proved by simulation, and all of them are successfully applied in underwater acoustic communication network simulation software.In addition, physical layer of underwater acoustic network is also simulated, the performance of the frequency-hopping communication system used of LDPC codes are verified by computer simulation in the Gaussian white noise channel, N-path certain channel and time-varying channel.The simulation test results show that the underwater acoustic network protocol stack which is established in the thesis can adapt to underwater acoustic channel environment, and it also can networking automatically, furthermore ,it is available to establish and maintain a stable routing. Moreover, it also can resist multi-user interference and exposed terminal problems in the media access control. Consequently, frequency hopping communication system based on LDPC codes shows better bit error rate compared with the system which based on traditional channel codes.